Operation principles of closed circuit oxygen rebreathers.

There are several ways in distinguishing closed circuit oxygen rebreathers. During my 3 year search for the various models I found new principles every time. I think the best way to categorize them is to look at the oxygen addition method and/or how oxygen is feed into the counter lung. Beside this method one could look to the various designs of scrubbers, hoses, valves, materials, age, companies, countries, application, military or civil or both, weight, for underwater use or not for underwater use and so on. The general list with models is based on the various countries were the rigs where made. You will find the "Main Index" button on top of every page to return to the index page with all models.
On this page you now find several design aspects listed with attached a photo or drawing to explain the aspect.
The physical and medical aspect of diving oxygen rebreathers are not a part of this publication. This because it is part of every good rebreather training. There are only a few things that you should keep in your mind when diving oxygen rebreathers:

• There is a depth limit of 6 meters.

• There is a debate if this could be 7,8 9 or even 10 meters

• The Russians dived 20 meters (many suffered an insult aswell)

• Dräger published a book with an article on divers escaping a submarine from 80 meters on pure oxygen. (You would do the same if you have no choice, but not for a hobby). (Stelzner, Tauchertechnik 1943)

• The 6 meter limit is considered to be safe.

• Never dive a oxygen rebreather alone.

• Flush the loop intensively before the dive to prevent a hypoxic loop

• Flush again every 15 minutes, during the dive!

• Only dive with certified oxygen conform medical standards.

• Use fresh absorbent as described by the rebreather manufacturer

• Do not rebuild any parts of the rebreather, unless you know what you are doing

• You must know the principle of: Hypoxia - Hyperoxia - Hypercapnia - CNS - UPTD -oxygentoxicity - tables to use with oxygen -oxygen service - and most important:

• Follow the course for your apparatus!

• Keep your rebreather away from grease

• Never touch parts which contact high pressure oxygen

• Only use oxygen compatible grease for high pressure fittings.

Main operating principles:

1. Manual addition

2. Constant Mass Flow (CMF)

3. On demand by counter lung operated valve.

4. On demand by IP regulator

5. Liquid oxygen generator

6. Chemical oxygen generator

Scrubber design: 

1. Axial design

2. Radial design

Counter lung position:

1. build in the counter lung

2. form, a bag or a bellow?

3. on the chest, on the back

4. scrubber and cooler

Counterlung design

1. The counterlung can be made as a single back

2. The counterlung can be split in inhale and exhale bag

3. The position of the counterlung vs. W.O.B (work of breathing)

Hoses

1. Single pendulum hose

2. Dual hose

3. Side mounted (fire fighting and mine rescue) (seitenschlauch)

Mouthpiece

1. Valve design

2. F.F.M (full face mask)

Bottles

1. Single or dual bottles

2. material

3. size

4. extra safety bottles

5. position, front - back

6. additional other mixes

Overpressure valves

1. On the lung

2. Position

3. Purpose

Weight belt

1. safety features

2. position

Special features:

1. Gas cooling systems

2. Alarm systems for low gas

3. Fog whiper in full face masks

4. Lamp on head of diver

5. Automatic inflator for unconscious diver

6. Gas switch to nitrox for deeper dives

7. Gas switch to trimix for even deeper dives

8. Communication equipment

9. Disposable canisters

10. Disposable scrubbers

11. Low magnetic features

12. Low acoustic features

13. Special suits for special operations.

Recent studies showed that even when the loop has been carefully flushed the average oxygen content is 76 %. If the partial pressure of oxygen should not exceed 1,6 bar a depth of 11,05 meter can be reached. If in extreme conditions the fraction of oxygen is 84% then a depth of 9 meter has same partial oxygen pressure. For safety reasons oxygen partial pressures should not exceed 1,4 bar. Calculated with a fraction of 76 % in the loop a depth of 8 meter is technically safe. For reasons of trim errors and variations in depth gauge precision 7 meter should be the safe limit. Flush every 15 minutes. This is my personal way of diving oxygen rebreathers. Never copy this when you have not done a specialized training on your model oxygen rebreather.
DO NOT COPY THIS ADVISE WITHOUT A TRAINING, mistakes will certainly kill you!